/Engine/Source/Runtime/ApplicationCore/Public/GenericPlatform/ITextInputMethodSystem.h
Gets the range of code point indices that are selected and which end of the selection the caret is at.
void GetSelectionRange ( uint32 & OutBeginIndex, uint32 & OutLength, [ECaretPosition](API\Runtime\ApplicationCore\GenericPlatform\ITextInputMethodContext\ECaretPosition) & OutCaretPosition )